Resistive element



RESISTIVE ELEMENT Filed Nov. 5, 1958 INVENTOR BY WMM ATTORNEYS UnitedStates Patent @fiiice 2,978,664 Patented Apr. 4, 1961 RESISTIVE ELEMENTGeolfrey King Walters, Dallas, Tex., assignor to Texas InstrumentsIncorporated, Dallas, Tex., a corporation of Delaware Filed Nov. 5,1958, Ser. No. 772,140 Claims. (Cl. 338-217) This invention relates tonovel resistive element which operates partially in the superconductingstate and partially in the normal conducting state and which has aresistance equal to any prescribed monotonically increasing function ofthe current through the resistive element.

Many kinds of non-linear resistive elements, the resistances of whichvary in a predetermined manner with the current flowing therethrcugh,are generally known. But prior to the present invention, there existedno simple circuit element the resistance of which could be prescribed tobe any monotonically increasing function. As a result, many functionswere not realizable at all by the use of simple circuit elements, butrequired multielement complicated electrical circuits The element of thepresent invention comprises an insulating body coated with a film ofmaterial which is maintained at a temperature at which the material ofthe film is superconducting. The diameter of the body of insulatingmaterial increases from one end of the element to the other. Whenoperating as a resistive element, the element is connected so thatcurrent flows from one end to the other. As the current is increased,the magnetic field associated with the cur-rent will increase. As themagnetic field increases, the superconductivity of the film will bedestroyed by this magnetic field starting from the end having thesmaller diameter and proceeding towards the end having the largerdiameter. Thus, by selection of the diameter of the device as a functionof the distance from the end having the smaller diameter, anymonotonically increasing dependence of resistance on current may beobtained.

Other objects and advantages of the invention will become readilyapparaent as the following description of the preferred embodimentunfolds and when taken in conjunction with the single figure of thedrawings which shows a cross sectional view of the circuit element ofthe invention.

As shown in the figure, the device comprises a base or body 11 ofinsulating material having a coating or film 12. The coating 12 is madeof material which becomes superconducting when the temperature of thematerial is sufiiciently low. Contacts 13 and 14 make electrical contactwith the film 12 at each end of the element. The conductors 15 and 16are electrically connected to the contacts 13 and 14. The conductors 15and 16 and the contacts 13 and 14 comprise a means to pass electricalcurrent through the film 12.

The cross section of the element is circular and the diameter of thecircular cross section increases from one end 17 to the other end 18.

Means are provided, not shown in the figure, to maintain the film 12 ata temperature at which the film would be superconducting. This could be,for example, a container of liquid helium in which the entire elementwould be immersed. When current flows through the element from one endto the other, a magnetic field will accompany the current. The strongerthe current, the more intense will be the magnetic field. When asuperconductor is placed in a magnetic field, it loses itssuperconductivity if the field is strong enough. The strongest magneticfield produced by the current flowing through the film 12 will existwhere the current density is the greatest. The current density is afunction of the diameter of the element and it will be greatest wherethe diameter is the smallest. Because the superconducting material isonly a thin film of material, a moderate amount of current flowingthrough this film will be accompanied by a magnetic field which willhave sufiicient strength to destroy the superconductivity of the film.For relatively low currents, the superconductivity will be destroyedonly at the end 17 of the element where the diameter is relatively smalland with increasing currents more superconductivity will be destroyedapproaching the end 18 having the large diameter. Thus, the distancefrom the small end of the element to which the superconductivity isdestroyed is a function of the current flowing through the element.Therefore, the impedance of the element will be a function of thecurrent. This function can be prescribed to be anymonotonically'increasing function simply by the choice of the shape ofthe element.

In a second embodiment of the present invention, the base or body 11 ofthe device may be of a material which becomes superconducting at lowtemperatures rather than of an insulator material. Thus, the resistiveelement disclosed herein may comprise a body of superconducting materialof the shape shown in Figure 1 with or without a thin coating of adiiferent superconducting material. The operation of either of thesealternative devices is essentially the same as the preferred embodimentdescribed above.

The above description is a preferred embodiment of the invention andmany modifications can be made thereto without departing from the spiritand scope of the invention which is limited only as defined in theappended claims,

What is claimed is:

1. A resistive element comprising a body of insulating material, a thincoating on said body, said coating comprising a material which becomessuperconducting below a given temperature, a means to maintain saidcoating below said given temperature, a first contact at one end of saidbody making electrical contact with said coating, a second contact atthe other end of said body making electrical contact with said coating,said body having a shape such that the diameter of the cross section ofsaid body increases from said one end of said body to said other end ofsaid body.

2. A resistive element comprising a body, a thin coating on said body,said coating comprising a material which becomes superconducting below agiven temperature, a first contact at one end of said body makingelectrical contact with said coating, a second contact at the other endof said body making electrical contact with said coating, said bodyhaving a shape such that the diameter of the cross section of said bodyvaries from said one end of said body to said other end of said body.

3. A resistive element comprising a body, a thin coating on said body,said coating comprising a material which becomes superconducting below agiven temperature, means to maintain said coating below said giventemperature, means for passing current through said coating from one endof said body to the other end of said body, said body having a shapesuch that the diameter of the cross section of said body variesfrom'said one end of said body to said other end of said body.

4. A resistive element comprising a body, a thin coating on said body,said coating comprising a material which becomes superconducting below agiven tempera ture, means for passing current through said coating fromone end of said body to the other end of said body, said body having ashape such that the diameter of the cross section of said body increasesfrom said one end of said body to said other end of said body.

5. A resistive element comprising a body of insulating material, a thincoating on said body, said coating comprising a material which becomessuperconducting below a given temperature, means for passing electricalcurrent through said coating from one end of said body to the other endof said body, said body having .a shape such that the diameter of thecross section of said body varies from said one end of said body to saidother end of said body.

6. A resistive element comprising a body, a thin coating on said body,said coating comprising a material that becomes superconducting below agiven temperature, means for passing current through said coating fromone end of said body to the other end of said body, said body having ashape such that the diameter of the cross section of said body variesfrom said one end of said body to said other end of said body.

7. A resistive element comprising a body of a material which becomessuperconducting below a given temperature, a thin coating on said body,said coating comprising a material which becomes superconducting below agiven temperature, a means to maintain said coating below said giventemperature, a first contact at one end of said body making electricalcontact with said coating, 21 second contact at the other end of saidbody making electrical contact With said coating, said body having ashape such that the diameter of the cross section of said body increasesfrom said one end of said body to said other end of said body.

8. A resistive element in which the resistance increases with anincrease in current passing therethrough, comprising a conical-likeshaped body, means on said body to cause the resistance of said elementto increase monotonically with an increase in the magnitude of theelectrical current passing through said element whenever said element issubjected to a temperature lower than a predetermined value, said meanscomprising a coating of material capable of superconductivity, and saidpredetermined value being the critical temperature at which saidmaterial becomes superconducting.

9. The combination, comprising a resistive body composed of a materialwhich becomes superconducting below a given temperature, means formaintaining said body below said given temperature thereby renderingsaid body normally superconducting, discrete portions of said body beingcharacterized by difierent cross-sectional areas so that the magneticfield produced by current flowing through the discrete portions of saidbody varies in intensity in a predetermined manner, and means forpassing current through the discrete portions of said body to establisha magnetic field surrounding the discrete portions capable ofselectively destroying the superconductivity of the discrete portions ofsaid body.

10. The combination according to claim 9 wherein said resistive bodydefines a thin film.

Thompson Mar. 3, 1936 Jacks et a1 Jan. 9, 1951

